多層建築物のコンクリート工事における型わく支柱による作業荷重の伝播と支柱の存置期間について (第 1 報)

Abstract

This report is regarding to thoretical analysis of loads distribution between reinforced concrete beam or slab and their shores during construction. If level of (k+3) story is concreted and each shores of (k+2) level are subjected to the loads, load increments of shores in (k+1) and k level can be calculated by linear equations, provided the coefficient of displacement of beam or floor, which is defined as displacement at a point when a unit load is added at another point, is calculated previously. Load decrements of shores in upper levels, which emerge on removal of shores in the lowest level, are also calculated by similar equations. Construction loads sustained by shores in some story are accumulation of the above increments and decrements of loads during construction. Conclusions of analysifs are as follows, (1) Usually, theoretical constraction loads sustained by the lowest shores are not over 1.0〜1.1, that are expressed as load ratio to the load sustained by the uppermost shore. Then, the maximum load ratio of the lowest beam or slab is usually 2.0〜2.1, including dead load 1.0. (2) The above load ratio is hardly dependent on number of shored levels, rate of construction, positions of shores, stiffness ratio of beam and slab, deformation ratio of shore, and so others. (3) Therefore, the safety factor in the lowest floor is mainly dependent on the design allowable load and the dead of floor concrete, that is, the thickness of slab in the uppermost level. Relationship between construction load artio to the long time allowable load, the thickness of slab, and the live load for design is shown as Fig. 21. (4) Construction loads, of which load ratio is over than 1.5 in Fig. 21, are over the short time allowable load inevitably. Then, in such a case the design allowable or the thickness of the slab must be modified in the design process. (5) Construction loads, of which load ratio is less than 1.5 but over than 1.0 in Fig. 21, are over the long time allowable load inevitably, but not over the short time allowable load. In such a case, minimum removal period of shores under slabs can be estimated graphically in Fig. 22-24. (6) The case, that construction loads are less than 1.0 in Fig. 21, do not appear in usual design. (7) The allowable load for beam design in Japanese Building Code, which is less than that for slab design, must be revised, because construction loads are severely over the allowable load for beam during construction.